1. Field of the Invention
This invention relates to a treatment on a silicon oxynitride, and more particularly, relates to a treatment of removing the silicon oxynitride.
2. Description of the Related Art
Silicon oxynitride (SiON) is often used on a polysilicon gate as an anti-reflection layer. A silicon oxynitride layer is a silicon rich film comprising many dangling bonds on the surface. Such a surface tends to form a layer of silicon dioxide (SiO2) when the surface is exposed to oxygen free radicals (O-*). For example, as a photo resist layer on a surface of a silicon oxynitride layer is removed by means of oxygen plasma, SiO2 is formed on the surface of the SiON layer. As a result, it is difficult to remove the silicon oxynitride layer, which lies underneath the silicon dioxide, by phosphoric acid in a latter segment of the process.
FIG. 1 depicts a molecular structure of a surface of a SiON layer, which comprises many dangling bonds 102. These dangling bonds 102 react easily with the oxygen free radicals in the surrounding to form a layer of SiO2 on the surface of the SiON layer. The SiO2 layer 202 covering the SiON layer 200 is illustrated in FIG. 2.
Although the phosphoric acid is very effective in removing the silicon oxynitride, it is rather ineffective in removing the silicon dioxide. Hence, it is difficult to remove the silicon oxynitride layer 200 located underneath the silicon dioxide layer 202 using the phosphoric acid, and is often resulted with silicon oxynitride residues.
A photo resist layer on a SiON layer is conventionally removed by an etching with oxygen plasma to the endpoint. An overetch is further conducted to completely remove the photo resist layer. A disadvantage with this approach is the oxygen plasma provides a source of oxygen and easily leads to a formation of a SiO2 layer on the surface of the SiON layer.
Accordingly, this invention provides a treatment on a silicon oxynitride surface, which is also applicable to a removal of a silicon oxynitride layer covered by a photo resist layer. Oxygen plasma is used to remove a majority of the photo resist layer, followed by an overetch using non-oxygen plasma to remove a residual of the photo resist layer.
Inert gas plasma is preferred for the non-oxygen plasma; and argon plasma is preferred among the inert gas plasma. The duration of the overetch is preferably in the vicinity of about 20% to about 25% of the duration of the oxygen plasma etching process.
The current invention also provides a method to remove a silicon oxide material, wherein the silicon oxide material is resulted from a reaction between silicon containing materials and oxygen plasma. By means of an ion bombardment method, the inert gas plasma is used to treat the silicon oxide material, and the inert gas plasma is preferred to be argon plasma.
The current invention also provides a method to remove a photo resist layer. The method is applicable in a removal of a photo resist layer covering a layer of silicon oxynitride. Oxygen plasma is used to remove a majority of the photo resist layer, followed by an overetch using non-oxygen plasma to remove a residual of the photo resist layer.
Inert gas plasma is preferred for the non-oxygen plasma; and the inert gas plasma is preferred to be argon plasma. The duration for the overtech is preferably in a vicinity of about 20% to about 25% of the duration of the oxygen plasma etching process.
The foregoing general descriptions are exemplary only, other additional advantages of the current invention are further disclosed in the following embodiment.